MIL-DTL-82655A
e. If precipitate forms correctly, add 200 ml of water, 20 ml of sulfuric -phosphoric acid mixture, and
6 to 8 drops of 0.2% barium diphenylamine sulfonate indicator. Titrate with standard potassium dichromate
solution, taking the sudden change from gray-green to blue as the endpoint. Run a blank determination with
the same reagents.
f. Calculate the wt% Fe2O3 on a calcined basis as follows:
Iron as Fe2O3, wt% =
0.07985 (V-v)N
x 100
W
where: V = Volume of potassium dichromate solution used to titrate sample, ml
v = Volume of potassium dichromate solution used to titrate blank, ml
N = Normality of potassium dichromate solution
W = Weight of ignited sample used, g
0.07985 = Milliequivalent weight of Fe2O3
g. Report the results of 2 determinations and their average.
4.5.4 Acidity. The acidity as wt% H2SO4 shall be determined in accordance with the following:
a. Weigh 10 ± 0.5 g of sample to the nearest 0.1 mg. Add 100 ml of distilled water and boil for
several minutes.
b. Filter and rinse sample with hot distilled water, adding rinsings to the filtrate.
c. Titrate the filtrate with 0.1N potassium hydroxide using methyl orange indicator.
d. Run a blank determination.
e. Calculate the acidity as wt% H2SO4 as follows:
Acidity as H2SO4, wt% =
0.04904 (V-v)N
x 100
W
where: V = Volume of potassium hydroxide solution used to titrate sample, ml
v = Volume of potassium hydroxide solution used to titrate blank, ml
N = Normality of potassium hydroxide solution
W = Weight of sample, g
0.04904 = Milliequivalent weight of sulfuric acid
f. Report the results of a minimum of 2 determinations and their average.
4.5.5 Specific Surface Area. The specific surface area shall be determined by multipoint B.E.T. nitrogen
adsorption in accordance with the methods outlined in ASTM Method D 3663 for Type II nitrogen adsorption
isotherms. Material shall be dried from 4.5.1. Instrumental conditions may vary between equivalent analyzers
and should be set in accordance with the manufacturer's instructions. Report the B.E.T. surface area
expressed in square meters per gram.
4.5.6 Particle Size. The particle size distribution shall be determined for information only. Measurement
of particle size distribution by a sedimentation method is preferred but not required. Report shall contain, at a
5
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